Just wait till your clock starts ticking.I'm 21 and I'm pretty sure I'm not changing my mind.

Personally, I'm 28, no kids, no desire for kids, far too dysfunctional to envisage it for the foreseeable future.
Luckily men are afforded the luxury of being able to make the choice later in life. I think I would like kids at some point but my life would have to be so radically different from now for me to conceive of it.